Risk factors for infection with and losses due to important parasites in gilthead sea bream and European sea bass aquaculture

The identification of risk factors for parasite introduction into and amplification within fish farms is crucial in order to design effective biosecurity and parasite control management strategies. Currently, there is a substantial lack of knowledge about such risk factors. A structured review of the available literature on risk factors for selected parasites was undertaken with the aim to bring together relevant knowledge on characteristics of host and parasite biology and risk factors for infection and amplification of parasites on fish farms. This process helped to assess the level of data available and identification of data gaps. Questionnaires were designed to provide parameter estimates on the relevance of risk factors for initial parasite infection and risk factors for infection causing impact for infection of gilthead seabream (Sparus aurata) with Enteromyxum leei and Sparicotyle chrysophrii, and of European seabass (Dicentrarchus labrax) with Ceratothoa oestroides and Amyloodinium ocellatum. Separate questionnaires were developed for each of parasite. Highly experienced experts were then invited to participate in a two-stage consultation process: participation in an online questionnaire, followed by a physical meeting. The responses obtained provide quantitative estimates for the relevance of risk routes of infection with the respective parasites, the relevance of management procedures for reducing or increasing mortality due to parasite infection, relevance of environmental factors, such as water exchange rate. Examples of risk factors that were relevant for development of infection causing impact were frequency of removal of mortalities from rearing units, number of cage farm sites in a production area. Management procedures that were identified to significantly reduce losses are separation of year classes during production, and fallowing. Furthermore, important quantitative estimates of impacts of parasite infection on aquaculture production in terms of delay in reaching harvest size or cumulative mortality during certain phases of production were obtained. The literature reviews and outcomes from the expert consultations are now forming the basis for planning further data collection through field studies. The information brought together will also feed into the development of biosecurity and integrated pest management strategies and assessments of the most economic management strategies of parasite infections. Funding of presentation: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 634429. This output reflects the views only of the author(s), and the European Union cannot be held responsible for any use which may be made of the information contained therein.